Expression and localization of basic fibroblast growth factor (bFGF) in the repair process of rat liver injury

Mesenchymal stromal cells isolated from human fetal liver release soluble factors with a potential role in liver tissue repair

We isolated a population of proliferating cells from cultured human fetal hepatocytes of 16-22 weeks gestational age. The cells shared a similar phenotype to that of mesenchymal stromal cells (MSCs) according to the International Society for Cellular Therapy (ISCT), including plastic adherence, antigen expression profile, and in vitro multilineage differentiation potential. Fetal liver (FL)-MSCs expressed the albumin gene, and harbored a subpopulation of CK18⁺ cells (20-40%), which defined their hepatic origin. However, when subjected to in vitro hepatic differentiation, FL-MSCs did not acquire significant liver functions. Quantitative analysis of conditioned medium (CM) collected from cultured cells revealed the presence of growth factors and chemokines with potential liver regenerative properties, the most relevant of which (concentration ≥3000 pg/ml) were SDF-1 alpha, IL-6, MCP-1, IL-8, MIP-1 beta, VEGF-A, Gro-alpha, and HGF. Culturing of FL-MSCs as spheroids significantly enhanced the secretion of HGF and bFGF (approximately 5-fold) compared with culture monolayers. Moreover, CM assessed in vitro induced capillary-like organization and migration of human umbilical vein endothelial cells (HUVECs) and fibroblasts as target cells. Interestingly, exosomes isolated from CM induced similar cellular responses in vitro with high efficiency and in a dose-dependent manner. FL-MSCs underwent several in vitro subcultivations, and did not stimulate allogenic T-cell proliferation thus suggesting a low immunogenicity. Furthermore, 5-year cryopreservation did not affect cell viability (approximately 90% of viable post-thawed FL-MSCs). These observations support the feasibility of a cell bank establishment for allogenic transplantation. We concluded that FL-MSCs or they secreted factors may be a valid alternative to hepatocyte transplantation in liver cell-based therapies.

Human adipose-derived mesenchymal stem cells promote recovery of injured HepG2 cell line and show sign of early hepatogenic differentiation

Currently, orthotopic liver transplantation is the gold standard therapy for liver failure. However, it is limited by the insufficient organ donor and risk of immune rejection. Stem cell therapy is a promising alternative treatment for liver failure. One of the most ideal sources of stem cells for regenerative medicine is adipose-derived stem cells (ADSCs). In this study, primary ADSCs seeded on cell culture insert were indirectly co-cultured with injured HepG2 to elucidate the role of ADSCs in promoting the recovery of injured HepG2 in non-contact manner. HepG2 recovery was determined by the surface area covered by cells and growth factor concentration was measured to identify the factors involved in regeneration. Besides, HepG2 were collected for q-PCR analysis of injury, hepatocyte functional and regenerative markers expression. For the ADSCs, expression of hepatogenic differentiation genes was analyzed. Results showed that non-contact co-culture with ADSCs helped the recovery of injured HepG2. ELISA quantification revealed that ADSCs secreted higher amount of HGF and VEGF to help the recovery of injured HepG2. Furthermore, HepG2 co-cultured with ADSCs expressed significantly lower injury markers as well as significantly higher regenerative and functional markers compared to the control HepG2. ADSCs co-cultured with injured HepG2 expressed significantly higher hepatic related genes compared to the control ADSCs. In conclusion, ADSCs promote recovery of injured HepG2 via secretion of HGF and VEGF. In addition, co-cultured ADSCs showed early sign of hepatogenic differentiation in response to the factors released or secreted by the injured HepG2.

Autoserum: An Optimal Supplement for Bone Marrow Mesenchymal Stem Cells of Liver-Injured Rats

Mesenchymal stem cells (MSCs) are an attractive source for the clinical cell therapy of liver injury. Although the use of adult serum, platelet lysate, or cord blood serum solves some of the problems caused by fetal bovine serum (FBS), the allogeneic immune response, contamination, and donor-to-donor and donor-to-receptor differences still obstruct the application of MSCs. In this study, the influences of autoserum from liver-injured rats (LIRs) and allogeneic serum from healthy rats on the isolation and culture of bone marrow MSCs (BMSCs) were examined and compared to FBS. The results showed that BMSCs cultured with autoserum or allogeneic serum exhibited better MSC-specific morphology, lower rate of cell senescent, and higher proliferation kinetics than those with FBS. In addition, autoserum promoted the osteogenic differentiation potential of BMSCs as allogeneic serum did. Although there were no significant differences in proliferation activity, immunophenotypic characterization, and differentiation potential between BMSCs cultured with autoserum and those with allogeneic serum, the potential adverse immunological reactions in patients with allogeneic material transplantation must be considered. We therefore believe that the autoserum from liver-injured patients may be a better choice for MSC expansion to meet the needs of liver injury therapy.

Effect of different liver resection methods on liver damage and regeneration factors VEGF and FGF-2 in mice

BACKGROUND

Different approaches to study liver regeneration in murine models have been proposed. We investigated the effect of different liver resection models on liver damage and regeneration parameters in mice.

METHODS

We compared the technical aspect of the 2 most commonly used techniques of 50% and 70% liver resection. Liver damage, as determined by the change in serum alanine aminotransferase and aspartate aminotransferase, as well as the regeneration parameters VEGF and FGF-2 were analyzed at 6 time points. A postoperative vitality score was introduced.

RESULTS

Cholestasis was not observed for either technique. Both resection techniques resulted in full weight recovery of the liver after 240 hours, with no significant difference between sham and resection groups. Postoperative animal morbidity and total protein levels did not differ significantly for either method, indicating early and full functional recovery. However, comparing the mitogenic growth factors FGF-2 and VEGF, a significant increase in serum levels and, therefore, increased growth stimulus, was shown in the extended resection group.

CONCLUSION

Extended resection led to a greater response in growth factor expression. This finding is important since it shows that growth factor response differs acdording to the extent of resection. We have demonstrated the need to standardize murine hepatic resection models to adequately compare the resulting liver damage.

Heparanase accelerates the proliferation of both hepatocytes and endothelial cells early after partial hepatectomy

BACKGROUND AND AIMS

Heparanase (HPSE) is an endo-β-D-glucuronidase, which cleaves heparan sulfate in the extracellular matrix (ECM) and has pro-angiogenic and pro-proliferative properties. The aim of this investigation was to study the effect of HPSE on hepatocytes and endothelial cells (EC) during liver regeneration.

METHODS

Following 70% hepatectomy (PHP), rats were injected daily with 1-50μg HPSE/rat. Liver samples were stained with H&E and anti-bromodeoxyuridine (BrdU) antibody. mRNAs of hepatocyte growth factor (HGF), stem cell factor, tumor necrosis factor (TNF)-α, interleukin(IL)-6, and cyclinD1 were tested by real-time qPCR. Matrix metalloproteinases (MMPs) were tested by gel zymography.

RESULTS

Compared to the saline control, HPSE increased hepatocyte proliferation 24h, 48h and 72h after PHP, with the maximal effect found at 24h with 50μg HPSE (40.9±2.5% vs. 8.6±4.3%, p<0.01 for BrdU staining; 5.5±0.9% vs. 0.8±0.5%, p<0.05 for mitosis). Proliferation of the sinusoidal and the portal vein radical ECs was also increased (p<0.05). HPSE caused a twofold increase in cyclinD1 mRNA (p<0.05) and in pro-MMP-9 levels (p<0.05). HPSE at all doses also caused significant reductions of TNF-α mRNA (p<0.05) and IL-6 mRNA, and no change in HGF mRNA.

CONCLUSIONS

HPSE enhances liver regeneration by inducing proliferation of hepatocytes and both sinusoidal and vascular ECs. Since the effect of HPSE on hepatocytes occurred earlier than that observed in ECs, this effect is not related to HPSE's effect on ECs. The mechanism of HPSE action is probably indirect and is mediated by HPSE-dependent ECM cleavage and the release of pre-existing enzymes.

Proteoglycan 4: a dynamic regulator of skeletogenesis and parathyroid hormone skeletal anabolism

Proteoglycan 4 (Prg4), known for its lubricating and protective actions in joints, is a strong candidate regulator of skeletal homeostasis and parathyroid hormone (PTH) anabolism. Prg4 is a PTH-responsive gene in bone and liver. Prg4 null mutant mice were used to investigate the impact of proteoglycan 4 on skeletal development, remodeling, and PTH anabolic actions. Young Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 4 to 21 days. Young Prg4 mutant mice had decreased growth plate hypertrophic zones, trabecular bone, and serum bone formation markers versus wild-type mice, but responded with a similar anabolic response to PTH. Adult Prg4 mutant and wild-type mice were administered intermittent PTH(1-34) or vehicle daily from 16 to 22 weeks. Adult Prg4 mutant mice had decreased trabecular and cortical bone, and blunted PTH-mediated increases in bone mass. Joint range of motion and animal mobility were lower in adult Prg4 mutant versus wild-type mice. Adult Prg4 mutant mice had decreased marrow and liver fibroblast growth factor 2 (FGF-2) mRNA and reduced serum FGF-2, which were normalized by PTH. A single dose of PTH decreased the PTH/PTHrP receptor (PPR), and increased Prg4 and FGF-2 to a similar extent in liver and bone. Proteoglycan 4 supports endochondral bone formation and the attainment of peak trabecular bone mass, and appears to support skeletal homeostasis indirectly by protecting joint function. Bone- and liver-derived FGF-2 likely regulate proteoglycan 4 actions supporting trabeculae formation. Blunted PTH anabolic responses in adult Prg4 mutant mice are associated with altered biomechanical impact secondary to joint failure.

Enhanced expression of fibroblast growth factor 2 in bone marrow cells and its potential role in the differentiation of hepatic epithelial stem-like cells into the hepatocyte lineage

The transplantation of bone marrow cells (BMCs) has been applied in liver regenerative cell therapy. However, details of the interaction between the transplanted BMCs and hepatic stem cells have not been elucidated. The aim of the present study was to investigate the interaction of BMCs with hepatic stem-like cells (HSLCs) and to determine the BMC factor that steers HSLC differentiation into the hepatocyte lineage. Both BMCs and HSLCs were obtained from an adult Sprague-Dawley rat, and a co-culture system was established. Cell proliferation was analyzed by a proliferation assay, and the differentiation of HSLCs into the hepatocyte lineage was evaluated by the detection of cellular mRNA for liver-specific proteins. DNA microarray analysis was applied to BMCs co-cultured with HSLCs to determine the genes upregulated by their interaction. The proliferation of HSLCs co-cultured with BMCs was significantly higher than that of HSLCs cultured alone, and the expression of mRNAs for both albumin and tryptophan-2,3-dioxygenase was detectable in the co-cultured HSLCs. DNA microarray analysis showed the upregulated expression of fibroblast growth factor 2 (FGF2) mRNA in BMCs co-cultured with HSLCs, and the expression of mRNAs for both albumin and tyrosine aminotransferase became detectable in HSLCs cultured with FGF2. Thus, BMCs stimulate both the proliferation of HSLCs and their differentiation into the hepatocyte lineage. FGF2 is one of the factors that is produced by the interacting BMCs and that stimulates this differentiation.

Compensatory growth mechanisms regulated by BMP and FGF signaling mediate liver regeneration in zebrafish after partial hepatectomy

Here, we describe the zebrafish (Danio rerio) as a vertebrate model system to study liver regeneration with the added benefit of its powerful genetics and screening possibilities to uncover the molecular pathways underlying liver regeneration. We developed a partial hepatectomy (PH) protocol in zebrafish and investigated in detail the cellular and morphological changes during the process of liver regeneration. We show that the type of regenerative response is dependent on the size of the injury sustained by the zebrafish liver. Furthermore, we demonstrate for the first time that the mechanisms of liver regeneration in zebrafish after PH are strikingly similar to those of rodents and humans, with 100% recovery of the liver mass after 6-7 d postsurgery. This occurs via compensatory growth mediated by proliferation of hepatocytes throughout the entire liver remnant. By analyzing transgenic fish expressing dominant-negative forms of either bone morphogenetic protein (BMP) receptor or fibroblast growth factor (FGF) receptor 1, we demonstrate that the BMP and FGF signaling pathways are crucial regulators of the early events during liver regeneration after PH. Our study demonstrates that the mechanisms of liver regeneration in zebrafish are highly similar to the processes ongoing during mammalian liver regeneration and make the adult zebrafish a suitable model system to study the mechanisms of liver regeneration.

Hepatic resection but not radiofrequency ablation results in tumor growth and increased growth factor expression

OBJECTIVE

The purpose of this study was to examine the effects of radiofrequency ablation (RFA) on tumor growth and growth factor expression in a murine model.

BACKGROUND

Surgical excision remains the only potentially curative therapy for hepatic malignancies. Tumor growth in the remaining liver may be accelerated after resection. The mechanism of this enhanced tumor growth remains unexplained, although growth factors that are released after hepatic resection (which facilitate liver regeneration) may play a role in residual tumor growth. RFA has become a viable alternative for patients who are not candidates for a curative resection. The effect of RFA on tumor growth and growth factor expression has not been studied.

METHODS

Hepatic tumors were established by direct injection with CT-26, a murine adenocarcinoma. Tumors were treated by either partial hepatic resection (PH) or RFA. Hepatocyte growth factor (HGF) and basic fibroblast growth factor (bFGF) expression was measured at selected time intervals post-treatment. Tumor growth was measured by reinjection of CT-26 into the residual liver after treatment. Nine days after reinjection, tumor volume was calculated and compared with nontreated controls.

RESULTS

HGF and bFGF expression was significantly higher at baseline in the CT-26 tumor-bearing mice when compared with non-tumor-bearing controls (P = 0.00001 and P = 9 x 10, respectively). There was an increase in HGF and bFGF expression at 24 hours (P = 0.005, and P = 0.001) in the PH group. In the RFA group, there was a decrease in HGF and bFGF expression at 24 and 72 hours (P = 0.001 and P = 0.002). Tumor growth comparisons revealed an increase in tumor growth in the hepatectomy group (P = 0.006) but not the RFA group (P = 0.2).

CONCLUSIONS

Baseline growth factor expression in tumor-bearing mice is exponentially higher when compared with non-tumor-bearing controls. HGF and bFGF expression are increased posthepatectomy, and decreased post-RFA. Partial hepatectomy results in an increase in tumor growth in the residual liver. RFA did not increase tumor growth after treatment. While hepatectomy is the only curative option for patients with hepatic malignancies, it may accelerate growth of microscopic residual disease.

Forced expression of hepatocyte-specific fibroblast growth factor 21 delays initiation of chemically induced hepatocarcinogenesis

Inappropriate fibroblast growth factor (FGF) signaling is involved in most tissue-specific pathologies including cancer. Previously we showed that inappropriate expression and chronic activity of FGF receptor (FGFR) 1 in hepatocytes accelerated diethylnitrosamine (DEN)-initiated hepatocarcinogenesis. Here we showed that although widely expressed FGF1 and FGF2 are frequently upregulated in hepatocellular carcinoma (HCC), germline deletion of both FGF1 and FGF2 had no effect on DEN-initiated hepatocarcinogenesis. Thus overexpression of FGF1 or FGF2 may be a consequence rather than contributor to hepatoma progression. FGF21 is the first of 22 homologues whose expression has been reported to be preferentially in the liver. We showed that similar to FGF1 and FGF2, FGF21 mRNA was upregulated in neoplastic and regenerating liver after partial hepatectomy (PH) and CCl4 administration. In situ hybridization analysis confirmed that in contrast to FGF1 and FGF2, expression of FGF21 mRNA was limited to hepatocytes. Forced overexpression of FGF21 in hepatocytes by gene targeting had no apparent impact on normal liver development and compensatory response to injury. Surprisingly, overexpression of FGF21 delayed the appearance of DEN-induced liver tumors. At 8 and 10 mo, only 10% and 30% of transgenic mice, respectively, developed adenomas compared to 50% (all adenomas) and 80% (60% adenoma/20% HCC) in the wild-type (WT) mice. However, the incidence and burden of HCC at 10 mo and later was equal in the FGF21 transgenic and WT mice. We propose that FGF21 may delay development of adenomas through activation of resident hepatocyte FGFR4 at early times, but counteracts the delay by acceleration of progression to HCC through interaction with ectopic FGFR1 once it appears in hepatoma cells. This indicates a dual function of FGF21 that may reflect changes in FGFR isotype during progression of differentiated hepatoma cells.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Ectopic activity of fibroblast growth factor receptor 1 in hepatocytes accelerates hepatocarcinogenesis by driving proliferation and vascular endothelial growth factor-induced angiogenesis

Fibroblast growth factor (FGF) signaling mediates cell-to-cell communication in development and organ homeostasis in adults. Of the four FGF receptor (FGFR) tyrosine kinases, only FGFR4 is expressed in mature hepatocytes. Although FGFR1 is expressed by hepatic cell progenitors and adult nonparenchymal cells, ectopic expression is commonly observed in hepatoma cells. Here, we determined whether ectopic FGFR1 is a cause or consequence of hepatocellular carcinoma by targeting a constitutively active human FGFR1 to mouse hepatocytes. Livers of transgenic mice exhibited accelerated regeneration after partial hepatectomy but no signs of neoplastic or preneoplastic abnormalities for up to 18 months. However, in diethylnitrosamine-treated mice, the chronic FGFR1 activity promoted an incidence of 44% adenomas at 4 months and 38% hepatocellular carcinoma at 8 months. No adenoma or hepatocellular carcinoma was observed in diethylnitrosamine-treated wild-type (WT) livers at 4 or 8 months, respectively. At 10 and 12 months, tumor-bearing livers in transgenic mice were twice the size of those in WT animals. Isolated hepatoma cells from the transgenic tumors exhibited a growth advantage in culture. Advanced hepatocellular carcinoma in the transgenic livers exhibited a reduced rate of necrosis. This was accompanied by a mean microvessel density of 2.7 times that of WT tumors and a markedly higher level of vascular endothelial growth factor. In cooperation with an initiator, the persistent activity of ectopic FGFR1 in hepatocytes is a strong promoter of hepatocellular carcinoma by driving cell proliferation at early stages and promoting neoangiogenesis at late stages of progression.

Pituitary Transcription Factor-1 Induces Transient Differentiation of Adult Hepatic Stem Cells into Prolactin-Producing Cells in Vivo

A subset of transcription factors function as pivotal regulators of cell differentiation pathways. Pituitary transcription factor-1 (Pit-1) is a tissue-specific homeodomain protein that specifies the development of pituitary somatotropes and lactotropes. In this study, adenovirus was used to deliver rat Pit-1 to mouse liver. Pit-1 expression was detected in the majority (50–80%) of hepatocyte nuclei after tail vein injection (2 × 109 plaque forming units). Pit-1 activated hepatic expression of the endogenous prolactin (PRL), GH, and TSHβ genes along with several other markers of lactotrope progenitor cells. Focal clusters (0.2–0.5% of liver cells per tissue section) of periportal cells were positive for PRL by immunofluorescent staining. The PRL-producing cells also expressed proliferating cell nuclear antigen as well as the hepatic stem cell markers (c-Kit, Thy1, and cytokeratin 14). These data indicate that Pit-1 induces the transient differentiation of hepatic progenitor cells into PRL-producing cells, providing additional evidence that transcription factors can specify the differentiation pathway of adult stem cells.

Angiogenesis in chronic inflammatory liver disease

Intrahepatic hypoxia may occur during the inflammatory and fibrotic processes that characterize several chronic liver diseases of viral and autoimmune origin. As a consequence, new vascular structures are formed to provide oxygen and nutrients. Angiogenesis involves a tightly regulated network of cellular and molecular mechanisms that result in the formation of functional vessels. Of particular importance are growth factors, molecules involved in matrix remodeling and cell migration, and vessel maturation-related factors. In recent years, a number of studies have examined the expression and function of many pro- and antiangiogenic molecules in the setting of nontumoral chronic liver diseases and liver regeneration. This review examines the potential pathogenetic role of angiogenesis in the context of viral hepatitis, cirrhosis, autoimmune hepatitis, primary biliary cirrhosis, and alcoholic liver disease. The future perspectives for research in this field are outlined.

Liver regeneration in FGF-2-deficient mice: VEGF acts as potential functional substitute for FGF-2

BACKGROUND/AIMS

The angiogenic properties, its role in mesoderm differentiation and cell culture studies implicate an important role of fibroblast growth factor (FGF-2) in liver regeneration. The aim of the study was to evaluate this role in a FGF-2 knockout mouse model.

METHODS

Liver regeneration after left hemihepatectomy (partial hepatectomy, PH) was evaluated in homozygous FGF-2 deficient (-/-) mice (male C57BL/6J) and their FGF-2 competent (+/+) littermates (controls) (day 0-10).

RESULTS

FGF-2-(-/-) mice displayed normal dynamics in liver regeneration. FGF-2 protein was overexpressed 4 days post PH in controls. BrdU incorporation showed a biphasic pattern in FGF-2-(-/-) mice, whereas it decreased continuously after one peak (day 2) in controls. In FGF-2-(-/-) livers hepatic growth factor mRNA post PH was 1 day longer decreased and markedly less elevated thereafter compared with control. Vascular endothelial growth factor (VEGF) mRNA levels were clearly increased in FGF-2-(-/-) mice pre- and postoperatively in contrast to controls. VEGF protein levels in livers of FGF-2-(-/-) mice were elevated preoperatively, but similar in both groups after PH. With SU5416, a VEGF-receptor inhibitor, liver regeneration in FGF-2-(-/-) mice was reduced significantly, whereas it remained unchanged in controls.

CONCLUSIONS

Liver regeneration dynamics in FGF-2-(-/-) mice were comparable with controls, potentially due to a functional substitution of FGF-2 by VEGF.

Quantitative analysis of the EGF receptor autocrine system reveals cryptic regulation of cell response by ligand capture

Autocrine signaling is important in normal tissue physiology as well as pathological conditions. It is difficult to analyze these systems, however, because they are both self-contained and recursive. To understand how parameters such as ligand production and receptor expression influence autocrine activity, we investigated a human epidermal growth factor/epidermal growth factor receptor (EGF/EGFR) loop engineered into mouse B82 fibroblasts. We varied the level of ligand production using the tet-off expression system and used metalloprotease inhibitors to modulate ligand release. Receptor expression was varied using antagonistic blocking antibodies. We compared autocrine ligand release with receptor activation using a microphysiometer-based assay and analyzed our data using a quantitative model of ligand release and receptor dynamics. We found that the activity of our autocrine system could be described in terms of a simple ratio between the rate of ligand production (VLT) and the rate of receptor production (VR). At a VLT/VR ratio of &lt;0.3, essentially no ligand was found in the extracellular medium, but a significant number of cell receptors (30-40%) were occupied. As the VLT/VR ratio increased from 0.3 towards unity, receptor occupancy increased and significant amounts of ligand appeared in the medium. Above a VLT/VR ratio of 1.0, receptor occupancy approached saturation and most of the released ligand was lost into the medium. Analysis of human mammary epithelial cells showed that a VLT/VR ratio of &lt;5×10−4was sufficient to evoke &gt;20% of a maximal proliferative response. This demonstrates that natural autocrine systems can be active even when no ligand appears in the extracellular medium.

Basic fibroblast growth factor stimulates repair of wounded hepatocyte monolayer: modulatory role of protein kinase A and extracellular matrix

The two important repair mechanisms after hepatocyte injury are proliferation and migration of the nearby healthy hepatocytes. Although previous studies have shown that basic fibroblast growth factor (bFGF) levels are markedly elevated after liver injury, the role of bFGF in the repair of the wounded hepatocytes is not well understood. The aim of this study was to delineate the role of bFGF in the repair of the wounded hepatocyte monolayers. Specifically, we examined the role of bFGF in cellular proliferation and migration of hepatocytes with an in vitro wound model. Standardized excisional wounds were created in clone 9 rat hepatocyte monolayers by a razor blade, and the extent of epithelial proliferation and migration was measured. After wound formation, bFGF (30 ng/mL) significantly stimulated proliferation of hepatocytes at the wound margin. bFGF also stimulated the migration of hepatocytes at the wound front. bFGF stimulation of hepatocyte migration correlated with increased formation of actin stress fibers and bFGF-receptor protein level. The bFGF stimulation of hepatocyte migration was abolished by various protein kinase A activating agents including 3-isobutyl-1-methylxanthine, 8-bromoadenosine-3', 5'-cyclic monophosphate, forskolin, and cholera toxin. In addition, protein kinase A activating agents almost completely prevented bFGF-induced actin stress fiber formation in the cells at the wound front. Varying the basement membrane composition of the extracellular matrix had a selective enhancing effect on the basal rates of hepatocyte migration (collagen IV > or = laminin > collagen I > fibronectin > control (plastic)). bFGF treatment resulted in a similar additive increase in hepatocyte migration across all coated surfaces studied. We conclude that bFGF promotes hepatocyte wound repair by stimulating both proliferation and migration of the hepatocyte at the margin of the wound.

Expression of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 in acute liver injury

BACKGROUND/AIMS

Matrix metalloproteinase-13, one of the principal neutral proteinases capable of cleaving native fibrillar collagens, is important in the degradation and remodeling of extracellular matrix. However, its precise expression in liver injury has not been characterized. We examined the kinetics of the expression of matrix metalloproteinase-13 and one of its specific inhibitors, tissue inhibitor of metalloproteinase-1, in acute liver injury in rats.

METHODS

Acute liver injury was induced by administration of carbon tetrachloride or two different doses of D-galactosamine hydrochloride in Wistar rats. Hepatic matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 mRNA levels were then examined by Northern blotting.

RESULTS

All rats survived after liver injury induced by carbon tetrachloride or low doses of D-galactosamine hydrochloride. However, rats died 5 days after induction of liver injury by high doses of D-galactosamine hydrochloride. In carbon tetrachloride-induced liver injury, matrix metalloproteinase-13 mRNA was transiently increased between 6 h and 1 day after injury. Tissue inhibitor of metalloproteinase-1 mRNA expression was increased between 6 h and 3 days after the peak of matrix metalloproteinase-13 expression. Similar patterns of matrix metalloproteinase-13 and tissue inhibitor of metalloproteinase-1 expression were observed in low-dose D-galactosamine hydrochloride-induced liver injury. In contrast, in high-dose D-galactosamine hydrochloride-induced liver injury, tissue inhibitor of metalloproteinase-1 expression peaked before matrix metalloproteinase-13 expression, which was increased 2 days after injury. Both mRNA levels continued to increase until death.

CONCLUSIONS

Transient expression of matrix metalloproteinase-13, followed by that of tissue inhibitor of metalloproteinase-1, was observed during recovery from acute liver injury induced by carbon tetrachloride and low-dose D-galactosamine hydrochloride. In contrast, disordered expression of matrix metalloproteinase-13 was observed in fatal liver injury caused by high-dose D-galactosamine hydrochloride. These results indicate that matrix metalloproteinase13 plays an important role in the early phase of recovery from liver injury.

Expressions of vascular endothelial growth factor in nonparenchymal as well as parenchymal cells in rat liver after necrosis

Vascular endothelial growth factor (VEGF) can induce proliferation of sinusoidal endothelial cells. Its mRNA expression was increased in proliferating rat hepatocytes in primary culture. To clarify a role of VEGF in liver after necrosis, expressions of VEGF and its receptors were measured in the liver or liver cells isolated from rats after carbon tetrachloride intoxication. Hepatic VEGF mRNA expression increased later than 24 h after the intoxication and became prominent at 168 h when liver necrosis disappeared, while hepatic mRNA expressions of its receptors increased between 24 and 72 h. VEGF mRNA expression was increased in Kupffer cells, hepatic macrophages and stellate cells isolated from rats between 24 and 72 h after the intoxication and in hepatocytes at 168 h compared to those cells from normal rats. Immunohistochemical VEGF stains were comparable to such results. Vascular endothelial cells existed abundantly in the necrotic areas, and sinusoidal endothelial cells appeared following disappearance of the necrotic areas. VEGF mRNA expression in hepatocytes isolated from 70% resected liver was increased at 12 h after the operation and became marked between 72 and 168 h. Similar increase of hepatic VEGF expression was immunohistochemically seen. In conclusion, VEGF derives from nonparenchymal as well as parenchymal cells in rat liver after necrosis. The former might contribute to vascular endothelial cell proliferation and the latter to sinusoidal endothelial cell regeneration.

Effects of neurotropic pyrimidine heterocyclic compound, MS-430, on cultured hepatic parenchymal and stellate cells

MS-430 is a novel synthetic pyrimidine derivative that stimulates regeneration of the nerve as a promoter for various growth factors such as epidermal growth factor (EGF) and nerve growth factor, and differentiation of astrocytes. The effects of MS-430 on the liver were tested using hepatocytes and stellate cells in primary culture isolated from rats. MS-430 enhanced EGF-induced DNA synthesis in hepatocytes while it alone failed to increase the basal DNA synthesis. Albumin mRNA expression in the cells and its amount in the medium were not changed by addition of EGF or MS-430 alone or both. Basic fibroblast growth factor (bFGF) increased DNA and but not collagen synthesis by hepatic stellate cells. Addition of MS-430 inhibited DNA synthesis by hepatic stellate cells at either presence or absence of bFGF, and collagen synthesis at the presence of bFGF. However, MS-430 had no effects on basal or bFGF-stimulated TGFbeta mRNA expression in the cells. These results suggest that MS-430 stimulated proliferation of hepatocytes as a comitogen for EGF without affecting albumin synthesis, and suppressed proliferation of activated hepatic stellate cells and their collagen synthesis without affecting TGFbeta expression.